1. Field of the Invention
The invention is concerned with an apparatus and process for equilibrating a hydrophilic liquid such as an aqueous solution with gas. More particularly the invention is concerned with such an apparatus for equilibrating standard solutions for preparation of standards useful in the determination of oxyhemoglobin dissociation curves and P.sub.50 (value of P.sub.0.sbsb.2 at which the hemoglobin is 50% saturated) determinations.
2. Prior Art
Generally, determinations of oxyhemoglobin dissociation curves, P.sub.50 determinations and the like are carried out on blood samples by analyzing the gases dissolved in the samples using an electrochemical blood gas analyzer.
In order to assure that the analyses of the dissolved gas in the blood samples are accurate the blood gas sample analyzer is generally calibrated against a standard solution made by contacting an aqueous solution with a gas sample of known concentration of for example oxygen, carbon dioxide and nitrogen. The instrument is then checked against two other samples of aqueous solutions which have been each equilibrated with other known mixtures of oxygen, carbon dioxide and nitrogen. Hence, while the instrument is calibrated against a single sample its accuracy is checked against usually two other known samples to assure that the instrument is operating properly.
A large percentage of medical laboratories which regularly analyze blood samples for gas concentration operate on a three shift or twenty-four hour basis. During each shift a different operator generally runs each gas analysis instrument. Thus, in a normal twenty-four hour day it is necessary to calibrate the instrument against the known sample and check it against two known standards three times, once for each eight hour shift. In case of power failures, other break downs or the like further calibration will be needed within each twenty-four hour day.
Generally the prior art apparatus for equilibrating an aqueous solution with a gas of a known composition has provided for relatively slow equilibration. One such instrument operates by introducing a gas of a known composition into a rotating sample tube whereby the surface area of the liquid being contacted with the gas is increased since the liquid is spread out against the sides of the tube as it rotates. Such an apparatus provides good equilibration but such equilibration will generally require about twenty to thirty minutes to time. Also, the apparatus must be re-used for each of the test samples which are to be prepared for checking the calibration of the instrument. Thus, with such an instrument it is necessary to equilibrate three samples with each equilibration taking about twenty to thirty minutes whereby about one hour of each eight hour shift is used up in preparing samples for standardizing the blood gas analyzer. Other available apparatus use such techniques as oscillation of the sample within a temperature controlled bath while a gas stream of known concentration is being flowed in contact with the liquid solution. In the oscillatory apparatus even slower attainment of equilibrium usually results.
The present invention is concerned with a gas equilibration apparatus which greatly cuts down time needed for preparing both a standard for calibrating a gas analyzer and the check or control solutions used to assure that the calibration of the instrument with the standard solution is correct.